Thermostatic switch



July 25, 1933. E. GETCHELL THERMOSTATIC SWITCH Filed June 6, 1932INVENTOR 85mm .M/N 1 E TCHELL Patented July 25, 1933' UNITED STATESPATENT? OFFICE BENJAMIN EVERETT GETCHELL, OF PLAINVILLE, CONNECTICUT,ASSIGNOR TO THE A CORPORATION OF CONNECTICUT THERMOSTATIC SWITCHApplication filed June 6,

tions upon a'predetermined change in tern perature.

Another object is to provide a thermostatic switch which will openand/or close the circuit with a snap action.

Another object is to provide a thermo-.

static switch which may be adjusted to vary the vtemperature at whichthe switch will operate to either open or close the circuit or to changethe direction of the flow of the c1rcuit.

In carrying out the invention I provide a bi-inetallic blade or arm ofsuitable construction, which arm is anchored at one end and carries acontact at the other end. A tension spring connects the movable andstationary ends of the arm in such a way that the movable end is movedto and held in either one of two positions by the tension of the springas well as by the normal bias of the arm.

The arm and spring are so designed and arranged that upon apredetermined change of temperature the contact carrying end of the armwill start to move from a normally bowed position and as soon as itpasses the medial line or straight position the spring will add itsforce to the Warping tendency of the arm and snap the movable end of thearm to anotherposition at the opposite side of the center. Therelatively stationary end of the arm is supported in such a manner thatit may be tilted for regulating or adjusting the action of the switch.

Fig. 1 is a side view of a switch embodying my invention.

, Fig. 2 is a front or plan'view of the same. Fig. 3 is a cross sectionon the plane of the line 33 of Fig. 2 but on a larger scale. Fig. 4 is aside view of the switch on the same scale as Fig. 3 and showing thethermo- 1932. Serial No. 615,524.

static arm in solid lines in one position and in dotted lines in anotherposition.

The parts of the switch are mounted on a support 6 which may be ofinsulating material and which will not warp or become distorted withordinary changes of temperature. 4

A thermostatic arm 7 is formed of any suitable bi-metallic strip and hasone end secured to a plate 8 which is normally stationary. The movableen-d of the arm carries a contact or contacts 9 adapted to engage thestops l0 and 11, either or both of which may be considered as stationaryelectrical contacts.

A helical spring 12 connects two points of the arm, one point being ator near the stationary end of the arm and the other point being near themovable contact carrying end of the arm.

Preferably the arm 7 is slotted at 13 to provide a mounting space havingample clearance for the spring. The arm normally has a biaswhich'slightly flexes or warps the arm and the spring 12 is so designedand arranged with respect to the arm that the spring tends to add ampleadditional flexure to the arm which is itself resilient. The tensionspring, therefore, adds its pressureto the normal flexing bias of thethermostatic spring arm.

lln order to adjust the switch so that it will operate at the desiredtemperature the relatively stationary end of the arm is made adjustable,for instance, by mounting it upon a tilting plate 8. This plate isprovided with an offset pivot or knife edge 14 which rests upon a plateor platform 15. This plate 8 with the attached thermostatic arm may berocked upon the projecting edge 14 and thus adjusted by tighteningand/or loosening the screws 16 and 17 which may have threaded engagementin the platform 15 or in the backplate 15. The plate 8 may be locked inthe desired position by means of the set screw 8 which has a threadedengagement either in plate 15 or 15.

The two stops or contact members 10 and 11 are also preferably madeadjustable, for instance, by forming them as threaded screws asv l8 and19, adjustable in the bracket 20 and the plate 21, respectively. Setnuts 22 and 23 may also be provided. The plate 21 may constitute acircuit terminal and the plate 24. may constitute another circuitterminal.

iihe thermostatic arm may be considered to be normally in the positionshown in full lines in Fig. where the bias of the arm and the tension ofthe spring 12 both tend to hold the contact end 9 bowed or warpedagainst the stationary stop or contact 10. Upon a predetermined changeof temperature the arm 7 will warp suiiiciently with respect to themedialline so as to just passthe center line and reverse its centralcurve so that the spring 12 instead tending to how the arm 7, as shownin full lines in Fig. 4, will be pulling on the other side of the centerline of the arm. and tend-to bow the arm into the position shown in dotand dash lines Obviously, after the active warping movement has oncestarted, the pressure of the contact carried by the thermostatic armagainst whichever stationary contact it may be engaged with, will beincreased until the thermostatic arm assumes a straight line form thusavoiding the usual vibrating or chattering movement of the contact.

The result of this action is that the contact end of the arm is snappedfrom one position to the other, thus breaking the circuit through thecontact 10 and establishing a new circuit through contact 11. Theopposite change of temperature will, of course, result in snapping thethermostatic arm back to its original position. Obviously, the contactand termi nals may be arranged to control other forms of wiringcircuits.

With such a construction it is possible to provide a quick-make andbreakswitch which may be actuated automatically and thermostatically by meansof change in temperature or by means of any other auxiliary means ofheating or cooling. By this construction it is possible to avoid thedisadvantages frequently found in thermostatic switches of slow andvibrating motion.

Obviously different forms of springs and difierent ways of securing thesprings to the respective ends of the thermostatic strip may be usedwithout departing from the spirit of my invention so long as thetendency of the spring is to assist the warping movement to either oneor both sides of a relatively straight line. I

' I claim:

1. A thermostatic switch including a onepiece bi-metallic strip havingan elongated closed ended slot therein intermediate its ends and atension spring in said slot, said spring being secured to said strip atthe respective ends of said slot and the axial center relate? of saidspring being in alignment with the edge center of said strip when saidstrip is in a straight line position.

2. A thermostatic switch including a Unitary lei-metallic strip havingan elongated slot therein intermediate its ends and a ten sion spring insaid slot, said spring being scoured to said strip at the respectiveends of said slot and the axial center of said spring being. inalignment with the edge center of said strip when said strip is in astraight line position, said spring tending to assist the warpingmovement of said strip.

3. A thermostatic switch including a onepiece bi-metaliic strip havingan elongated slot therein intermediate its ends and a tension spring insaid slot, said spring being secured to said strip at the respectiveends of said slot and the axial center of said spring being in alignmentwith the edge center of said strip when said strip is in a straight lineposition, said spring tending to assist the warping movement of thestrip as soon as said strip has warped beyond a relatively straight lineposition.

4. A. thermostatic switch including a unitary bi-metallic strip havingan elongated slot therein intermediate its ends and a tension spring insaid slot, said spring being secured to said strip at the respectiveends of said slot and the axial center of said springs being inalignment with the edge center of said strip when said strip is in astraight line position, said spring tending to assist the warpingmovement of said strip on both sides of the center line with respect tothe warping movement of said strip.

5. A thermostatic switch including a single bi-Inetallic strip having anelongated slot therein intermediate its ends said slot being closed atboth ends and'a tension spring in said slot, said spring being securedto said strip at the respective ends of said slot and the axial centerof said spring being in alignment with the edge center of said stripwhen said strip is in a straight line position, said strip being securedto a relatively fixed mounting at one of said ends and having its otherend free to warp to make or break an electrical contact.

6. A thermostatic switch including an ad justable tilting member havinga knife edge support, a bi-metallic strip having one end carriedthereby, stops for the opposite end of said strip, a tension springconnecting two portions of the strip and tending to bend the strip andan adjustable abutment for said tilting member consisting of two screwsone on each side of the knife edge support-for adjusting the tiltingmember and maintaining it in its adjusted position.

BENJAMIN EVERETT GETCHELL.

